This application is based on European Patent Application No. 99830489.3 filed on Jul. 30, 1999, the content of which is incorporated hereinto by reference.
The present invention relates to a composition sensitive to IR radiation and to heat, and a lithographic plate coated with this composition.
In particular, it relates to a composition sensitive to IR radiation and to heat which is useful for the production of a lithographic plate of the positive type.
It also relates to a composition sensitive to laser radiation which is useful for the production of a lithographic plate of the positive type.
As is well-known, the technique of printing by means of lithographic plates is based on differential partition between fatty substances and water. The fatty substance or ink is retained preferentially by the image area and the water is preferentially retained by the non-image area. When the surface of a lithographic plate, suitably prepared, is moistened with water and then sprinkled with ink, the non-image area retains the water and repels the ink, while the image area accepts the ink and repels the water. Then, the ink on the image area is transferred onto the surface of a material on which it is desired to reproduce the image, such as, for example, paper, textile and the like.
In general, the lithographic plates used in printing processes are formed from an aluminium support covered with a composition sensitive to light (photosensitive). When such a composition becomes soluble in an alkaline developing bath through the action of heat or of radiation of appropriate wavelength, the printing process is termed xe2x80x9cpositivexe2x80x9d. Conversely, when the portion exposed to heat or to radiation of appropriate wavelength becomes insoluble in an alkaline developing bath, the printing process is termed xe2x80x9cnegativexe2x80x9d. In both cases, the remaining, image area is lipophilic and hence accepts the ink, while the non-image area is hydrophilic and accepts the water.
The recent developments in the field of lithographic plates have been directed towards the search for compositions sensitive to laser light, preferably in the near IR. In particular, to laser light controlled by software, in such a way as directly to transfer the image created by computer onto the surface of the plate. This technique has the advantage of eliminating the photographic films, with consequent reduction in the pollution due to the chemical substances used for the preparation and production of these and elimination of all the problems that arise in the transfer of the image onto the plate via photographic films.
In the first place, a composition sensitive to radiation emitted by a laser could impart greater reliability to the system.
Secondly, it would be possible to work under ambient illumination, thus eliminating the automatic loading systems or the darkrooms.
With the aim of attaining this objective, in recent years many compositions comprising a polymeric binder and a solubility inhibitor have been investigated. Such a solubility inhibitor has the ability to render the polymeric binder insoluble in a suitable alkaline developing bath as long as it has not been exposed to a sufficient quantity of heat and of then rendering it soluble in the said developing bath after such exposure to heat. Besides the aforesaid components, many of the compositions described until now also comprise a so-called IR absorber, usually consisting of a compound capable of absorbing IR radiation and of transforming part of the radiation absorbed into heat, giving it up to the immediately surrounding environment.
The present invention aims to provide a composition sensitive to heat and a lithographic plate of the positive type coated with the said composition wherein the solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof.
The present invention also aims to provide a composition sensitive to IR radiation and a lithographic plate of the positive type coated with the said composition wherein the solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof.
The present invention also aims to provide a composition sensitive to laser radiation and a lithographic plate of the positive type coated with the said composition wherein the solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof.
The term xe2x80x9clithographic platexe2x80x9d means a support covered with a coating which, after being suitably exposed and developed, is used, as a planographic matrix, in printing processes wherein there is differeritial partition between fatty substances and water.
Typical examples of support materials are constituted by plates of aluminium, zinc, copper, polyester and paper covered with a polymer. Preferably, the support is a sheet of grained aluminium, oxidized and suitably treated to receive the photosensitive composition.
The term xe2x80x9cpositive typexe2x80x9d means that the portion of the photosensitive coating exposed to the radiation or to heat becomes soluble in such a way that it can be removed during the process of development of the plate. Typically, the development process is performed in alkalis having a conductivity pf from 75 to 110 mS.
The term xe2x80x9cpolymeric binderxe2x80x9d means a polymer soluble in alkali, such as for example a novolac resin, a resol resin, a vinylphenolic resin, derivatives thereof or mixtures thereof.
Typically, a novolac resin is a polycondensation product obtained by reaction in an acidic environment between formaldehyde and phenol and/or m-cresol and/or symmetrical xylenol in a molecular ratio of less than 1 (for example formaldehyde:phenol=1:2). Optionally, the thus obtained compound is variously modified such as, for example, by reaction with amides.
Typical examples of commercial novolac resins are the products LB 6564 (mean ponderal molecular weight=6000-10,000) and LB 744 (mean ponderal molecular weight=8000-13,000) from the firm Bakelite (Germany), R 7100 (mean ponderal molecular weight=8000-10,000) from the firm Rohner, and PN 320 (mean ponderal molecular weight=3000-5000) and PN 430 (mean ponderal molecular weight=5000-9500) from the firm Clariant; 010/129/2 (mean ponderal molecular weight=8700-9700), 010/129/1 (mean ponderal molecular weight=2200-32 00), and 010/127/1 (mean ponderal molecular weight=800-1800), 76/159 (mean ponderal molecular weight=2900-3900), 76/160 (mean ponderal molecular weight=2200-3200), 76/190 (mean ponderal molecular weight=7500-8500) from the firm Rohner.
The term xe2x80x9cheat-sensitive compositionxe2x80x9d means a composition which includes a polymeric binder and has the property of being insoluble in an alkaline developing bath as long as it has not been exposed to a sufficient quantity of heat and of then being soluble in the said bath after such exposure to heat.
The term xe2x80x9csolubility inhibitorxe2x80x9d means a compound capable of rendering a heat-sensitive composition that contains it insoluble in a suitable alkaline developing bath as long as the said composition has not been exposed to a sufficient quantity of heat and/or laser radiation and of then rendering it soluble in the said developing bath after such exposure to heat and/or laser radiation.
The term xe2x80x9chydroxyl numberxe2x80x9d means the number of milligrams of KOH equivalent to the hydroxyl content of 1 gram of the compound under test. The determination is made by acetylating the compound under test with acetic anhydride in pyridine, hydrolysing with water the excess acetic anhydride that has not reacted and titrating the free acetic acid with KOH (phenolphthalein indicator).
The term xe2x80x9cacidity numberxe2x80x9d means the number of milligrams of KOH necessary to neutralize the free acid present in 1 gram of the compound under test.
The term xe2x80x9cIR absorberxe2x80x9d means a compound capable of absorbing IR radiation and of transforming part of the absorbed radiation into heat and giving it up to the immediately surrounding environment. Preferably, such an absorber is soluble in water, ketones, glycols, glycolethers, alcohols, esters and mixtures thereof.
Typical examples of absorbers are the commercial products KF 646, KF 645, KF810, KF 1003, KF 1002, IR HBB 812 and KF 818 from the company Riedel-de Haen/Allied/Signal (Seelze, Germany), the commercial product ADS 830A and ADS 1060A, ADS793EI, ADS798MI, ADS798MP, ADS800AT, ADS805PI, ADS805PP, ADS805PA, ADS805PF, ADS812MI, ADS815EI, ADS818HI, ADS818HT, ADS822MT, ADS838MT, ADS840MT, ADS845BI, ADS905AM,ADS956BGI, ADS1040P, ADS1054P, ADS1050P, ADS1120P from the firm American Dye Source (Varennes, Quebec, Canada), the commercial products YKR-3070, YKR-3082, D99-029 and D99-039 from the firm Yamamoto Chemical Inc., the commercial product Projet 825 LDI from the firm Avecia Limited (ex Zeneca Specialties, Manchester, England). Here, for convenience, the product Projet 825 will be referred to hereinbelow by the abbreviation xe2x80x9cZxe2x80x9d.
A particularly interesting family of absorbers is that characterized by the following structural formula: 
wherein X, Y, R, Rxe2x80x2 and Rxe2x80x3 can take many meanings. Typical examples of these meanings are: simple or condensed heterocyclic ring for X, simple or fused heterocyclic ring for Z and Y together with the carbon atom to which they are bound, hydrogen, C1-3 alkyl, SO3xe2x88x92 or COOxe2x88x92 for R and Rxe2x80x2 independently of one another and H or Cl for Rxe2x80x3.
Particular examples of the said heterocyclic rings are: 
Specific examples of absorbers are: 
The term xe2x80x9cIR radiationxe2x80x9d means radiation of a wavelength of from of from 780 to 1400 nm.
A typical example of a device used to generate IR radiation is a laser diode which emits at ca. 830 nm.
The term xe2x80x9claser radiationxe2x80x9d means radiation of a wavelength of from 600 to 1400 nm.
Absorber capable of absorbing radiation having a wavelenght of from 600 to 780 nm are well known in the art. Typical examples of such absorbers are the commercial products ADS640PP, AD640HI, ADS640HI, ADS675MT, ADS680BP, ADS740PP, ADS745HT, ADS760MP, ADS775MI, ADS775MP, ADS775HI, ADS775PI, ADS775PP, ADS780MT and ADS780BP from the firm American Dye Source (Varennes, Quebec, Canada).
The term xe2x80x9cnominal wavelengthxe2x80x9d means a wavelength of from 805 to 830 nm.
The term xe2x80x9cdyexe2x80x9d means a coloured compound or preparation capable of dyeing the photosensitive composition in order to reveal the image after the exposure to light and/or after development.
Typical examples of dyes are Basonyl(trademark) blue 636 (Colour Index 42595) from the firm Basf (Germany), Sudan Yellow 150 (Colour Index 11021) from the firm Basf (Germany), Solvent Green 3 (Colour Index 61565), Solvent Blue 59 (Colour Index 61552), Solvent Blue 35 (Colour Index 61554) or mixtures thereof.
The term xe2x80x9ctriazinexe2x80x9d intends to mean the entire family of the substituted trichloromethyl-s-triazines of known type.
The term xe2x80x9cadditivexe2x80x9d means a compound used to improve or confer a desired property on the photosensitive composition such as for example an enhancer developing agent, a pigment, a plasticizer capable of rendering the emulsion less resistant to heat and hence more sensitive, without however having an insolubilizing function, or an agent capable of modifying the surface and/or interfacial tension and thus improving the spreadability characteristics on the support and the covering power of the heat-sensitive composition.
Typical examples of pigments are: Heliogen(trademark) Blue L 6700 F (PB 15:6 colour index 74160), Heliogen(trademark) Blue L 6875 F (PB 15:2 colour index 74160) from the firm Basf (Germany), and from the Waxoline(trademark) series: BLUE AP FW (colour index SB 36 PART 2 61551), VIOLET A FW (colour index SV 13 PART 2 60725), GREEN G FW (colour index SB 3 PART 2 61565) from the firm Avecia Limited (ex Zeneca Ltd.) or mixtures thereof.
Typical examples of agents capable of modifying the surface and/or interfacial tension are the copolymers dimethylpolysiloxane-modified polyethers, mixtures of high-boiling aromatic solvents, ketones and esters and fluorinated surfactants. Typical examples of such agents are the commercial products BYK 300, 302 and 341, BYKETOL(trademark) OK from the firm BYK Mallinckrodt and FC 430 and FC 431 from the firm 3M.
In a first aspect thereof, the present invention relates to a heat-sensitive composition of the positive type comprising a polymeric binder and a solubility inhibitor, characterized in that the said solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof wherein some hydroxyl groups have been esterified with a carboxylic acid or a reactive derivative thereof.
In a second aspect thereof, the present invention also relates to a lithographic plate of the positive type coated with a heat-sensitive composition comprising a polymeric binder and a solubility inhibitor, characterized in that the said solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof wherein some hydroxyl groups have been esterified with a carboxylic acid or a reactive derivative thereof.
In a third aspect thereof, the present invention relates to a laser sensitive composition of the positive type comprising a polymeric binder and a solubility inhibitor, characterized in that the said solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof wherein some hydroxyl groups have been esterified with a carboxylic acid or a reactive derivative thereof.
In a further aspect thereof, the present invention also relates to a lithographic plate of the positive type coated with a laser composition comprising a polymeric binder and a solubility inhibitor, characterized in that the said solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof wherein some hydroxyl groups have been esterified with a carboxylic acid or a reactive derivative thereof.
Typically, the said hydroxylated acrylic copolymer has a hydroxyl number of from 40 to 200, preferably from 100 to 170.
Advantageously, the said hydroxylated acrylic copolymer has a mean ponderal molecular weight (MW) of from 3000 to 30,000 atomic mass units (a.m.u.) and, preferably, from 6000 to 20,000 a.m.u. and has a polydispersity index (MW/Mn) of from 1.5 to 6.
Typical examples of suitable hydroxylated acrylic copolymers are the Macrynal(trademark) resins from Hoechst, such as, for example, Macrynal(trademark) SM 510 N (hydroxyl number: 135-155), SM 513, (hydroxyl number: 110-130), SM 515 (hydroxyl number: 145-160) and SM 516 (hydroxyl number: 130-150).
Typical examples of suitable carboxylic acids are the aliphatic and aromatic mono- and polycarboxylic acids. Advantageously, the acid is a dicarboxylic acid selected from the group consisting of maleic, fumaric, malonic and phthalic acid.
Typical examples of reactive derivatives of aliphatic carboxylic acids are those selected from the group consisting of acid chloride and anhydride.
Advantageously, the hydroxylated polymer according to the present invention is modified by partial esterification with maleic anhydride.
Preferably, the said partial esterification is performed using from 10 to 90% of the stoichiometric quantity of the reactive aliphatic carboxylic acid derivative required to esterify all the hydroxyl groups of the hydroxylated polymer. More preferably from 20 to 60%, still more preferably from 20 to 30%.
The said esterification reaction of some hydroxyl groups of a hydroxylated polymer with an aliphatic carboxylic acid or a reactive derivative thereof is readily performed by standard techniques well known to the specialist in the field.
Preferably, the said polymeric binder comprises a novolac resin having a mean ponderal molecular weight of from 2000 to 14,000.
Advantageously, the said polymeric binder consists of a mixture of two or more novolacs. Preferably, a first novolac has a mean ponderal molecular weight of from 3000 to 5000 and a second novolac has a mean ponderal molecular weight of from 6000 to 10,000.
In a preferred embodiment of the present invention, the composition also comprises an IR absorber capable of absorbing IR radiation of from 780 to 1400 nm, preferably from 780 to 1100 nm, and of converting it into heat.
The composition of the present invention can also comprise a dye.
Typically the said dye is Basonyl blue 636 (Colour Index 42595) and is present in quantities sufficient only to dye the composition.
The composition of the present invention can also comprise a plasticizer, a triazine and other additives of a standard nature. In particular, the plasticizer has the purpose of modifying the toughness and the hardness of the said composition by varying its sensitivity to heat without appreciably affecting its sensitivity to the developers.
Advantageously, the composition of the present invention can also contain solubility inhibitors belonging to other classes such as, for example, organometallic compounds and organic salts of metals which are the subject of another patent application, which is included here by reference, filed on the same date by the Applicant. Typically, the said compositions are organic derivatives of titanium. A typical example of such compounds is triethanolaminated titanium isopropoxide, also known as Tyzor(trademark) TE.